The present invention relates generally to a hard-facing alloy, and more particularly, the invention relates to a cobalt-free hard-facing alloy.
Hard-facing alloys are used for a variety of applications including: valve seats, valve stems, turbine blades, lawn-mower blades, mixers, rollers, grinders, cutters, etc. These alloys offer a variety of properties including: high galling resistance, good wear resistance, high strength and erosion performance, corrosion performance, and high hardness. Most hard-facing alloys fall into one of three alloy categories: iron-based, nickel-based, and cobalt-based alloys. Cobalt-based alloys have been the industry standard for valve hardfacing applications for almost 50 years now, largely in-part due to their versatility over a wide range of applications. The two most notable of these are STELLITE 6 and 21. Unfortunately, for nuclear applications, these alloys tend to wear away with time and form radioactive isotopes such as Co58 and Co60.
During the past two decades, considerable attention has been placed on iron-based alloys, essentially modified-stainless steels, as these alloys can eliminate the concern of radiation build-up while still offering excellent wear, galling, and corrosion performance. Several iron-based, cobalt-free, “modified-stainless steels” are currently used by the nuclear industry primarily for valve seat applications including: NOREM, GALLTOUGH PLUS, NITRONIC 60, and TRISTELLE 5183. These alloys have met with limited success for various reasons including: solidification cracking during welding, poor weldability, cracking in service, poor wear properties at service temperatures, and poor acceptance by industry in general. Compositional analysis and phase stability calculations using today's more advanced prediction tools have described why many of these alloys have failed to meet the rigorous industry standards and applications.
Accordingly, there is a need for an improved alternative cobalt-free hard-facing alloy for use in the nuclear industry as well as other industries.